Historically, the performance of an internal combustion engine has been limited by fixed valve lift profiles, i.e., fixed timing of the opening and closing of the valves relative to the angular position of the engine crankshaft and fixed lift of the valves. However, modern internal combustion engines may utilize one of several methods and/or devices to vary the valve lift profile to, at least in part, control the flow of gas and/or air into and/or out of the engine cylinders. Modern internal combustion engines may utilize devices, such as, for example, variable valve actuating mechanisms, two-step cam profile switching mechanisms (i.e., variable valve lift devices (VVL)), and deactivation valve lifters to vary the amount by which the valves of an engine are lifted (i.e., opened). Furthermore, engines may utilize devices, such as variable valve actuating mechanisms and cam phasers, to vary the timing of the opening and/or closing of the engine valves relative to the angular position of the engine crankshaft.
Two-step cam profile switching mechanisms utilize a two-step cam profile switching device, such as, for example, a two-step roller finger follower (RFF), to switch between two discrete valve lift profiles depending at least in part upon engine operating conditions and/or parameters. Two-step systems are relatively simple and are operable over a relatively wide range of engine operating speeds. Further such systems are relatively easy to package on new and even existing engines. By operating the two-step cam profile switching mechanism in conjunction with a cam phaser a wide range of variation in the valve lift characteristic is obtained. The valve lift profile is selected via the two-step cam profile-switching device, and the timing of the valve lift is adjusted and/or varied by the cam phaser.
Currently there are no reliable methods of reliably determining whether one or more of the two-step cam profile switching mechanisms used in an internal combustion engine are in the wrong mode of operation while the engine is cranking and running. One method that currently exists is a hands-on approach, which involves a visual inspection of the two-step cam profile switching mechanism during cranking of the engine, which requires the removal of a substantial portion of the top of engine hardware. A second hands-on approach is a cranking compression test that involves installing a compression tester into each of the spark plug holes, cranking the engine, and measuring the in-cylinder air pressure. Both of the hands-on approaches requires that a person, such as an automobile mechanic, conduct the diagnostic testing and is therefore not a method that is readily applicable to running real-time in an embedded controller.
Another method involves embedding real-time algorithms that use an exhaust oxygen sensor and are therefore ineffective when the engine is not running at stoichiometry. Therefore, the mode of operation of the two-step cam profile switching mechanism could be mis-diagnosed or undiagnosed, which may result in emissions non-compliance or the failure of the two-step cam profile switching mechanism or the engine.
What is needed in the art is a reliable and real-time method for determining whether a two-step variable valve lift device is operating in the improper mode of operation.
It is a principal object of the present invention to provide a reliable and real-time method for determining whether a two-step variable valve lift device is operating in the improper mode of operation.